Radio communication apparatus capable of switching modulation schemes

ABSTRACT

A transmitting apparatus, includes a signal generator that generates a modulation signal by modulating transmission data using one of a plurality of modulation schemes, a first modulation scheme having a higher m-ary modulation value than other modulation schemes and a pilot signal generator generates a pilot signal. An orthogonal frequency division multiplexing (OFDM) signal generator generates an OFDM signal by selecting the modulation signal and the pilot signal according to the frame timing signal. The OFDM signal is converted to a radio signal, is amplified and is transmitted to an antenna. The pilot signal is inserted in the OFDM signal per a predetermined OFDM symbol and per a predetermined subcarrier and has a lower amplitude than a maximum amplitude of the first modulation scheme in an in-phase-quadrature (IQ) plane.

This application is a continuation of U.S. patent application Ser. No.13/093,301, filed Apr. 25, 2011, now U.S. Pat. No. 8,218,680, issuedJul. 10, 2012, which is a continuation of U.S. patent application Ser.No. 12/757,509, filed Apr. 9, 2010, now U.S. Pat. No. 7,953,177, issuedMay 31, 2011, which is a continuation of U.S. patent application Ser.No. 11/336,956, filed Jan. 23, 2006, now U.S. Pat. No. 7,738,590, issuedJun. 15, 2010, which is a continuation of U.S. patent application Ser.No. 09/978,662, filed Oct. 18, 2001, now U.S. Pat. No. 7,023,933, issuedApr. 4, 2006, the disclosures of which are expressly incorporated hereinby reference in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a digital modulation method for use inradio communications.

In a digital mobile radio communication method, transmission andreception between a base station apparatus and communication terminalapparatus is influenced by the radio wave propagation environment, andthe radio wave propagation environment influences reception quality andreception sensitivity characteristics on the receiving side. In thisregard, heretofore, a method relating to the pilot symbol signal pointposition when performing quasi-coherent detection has been presented inthe document, Rayleigh Fading Compensation Method for 16QAM MODEM inDigital Land Mobile Radio Systems, SAMPEI, Transactions of the Instituteof Electronics, Information and Communication Engineers B-II, Vol.J-72-B-II, No. 1, pp. 7-15, January 1989, as a method of improving thereception sensitivity characteristics of a receiving apparatus bydevising a pilot symbol signal point position. FIG. 1 shows the signalpoint arrangement of 16QAM symbols and pilot symbols in thein-phase-quadrature plane (IQ plane). In FIG. 1, reference code 3501indicates a 16QAM signal point in the IQ plane, and a method is knownwhereby the signal point that has the greatest amplitude among 16QAMsignal points is taken as a pilot signal, such that a pilot symbolsignal point is placed at one of reference code 3502, reference code3503, reference code 3504, and reference code 3505, and quasi-coherentdetection is performed.

However, with conventional pilot symbol arrangement, a signal point withthe greatest signal point amplitude of signal points in one modulationmethod is taken as a pilot symbol signal point, but when the receptionsensitivity of the receiving apparatus is considered, this point is notnecessarily at the optimum position for a pilot symbol signal point.Also, increasing the transmission power of the transmitting apparatus toimprove the reception sensitivity characteristics of the receivingapparatus, and increasing the maximum signal amplitude shown in FIG. 1,means increasing the transmission power for all symbols to betransmitted, and thus increasing the power consumption of thetransmitting apparatus.

SUMMARY OF THE INVENTION

It is an objective of the present invention to arrange pilot symbolsignal points while maintaining the average transmission power of atransmitting apparatus at a fixed level, and to improve the receptionsensitivity characteristics of a receiving apparatus.

The present invention achieves the above objective by using a methodwhereby pilot symbol signal points are arranged in thein-phase-quadrature plane (IQ plane) so that the reception sensitivityof a receiving apparatus becomes optimal.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the invention will appearmore fully hereinafter from a consideration of the following descriptiontaken in connection with the accompanying drawing wherein one example isillustrated by way of example, in which;

FIG. 1 is a drawing showing 16QAM symbol and pilot symbol signal pointarrangement in the IQ plane;

FIG. 2 is a drawing showing an example of a frame configurationaccording to Embodiment 1 of the present invention;

FIG. 3 is a block diagram showing the configuration of a transmittingapparatus according to Embodiment 1 of the present invention;

FIG. 4 is a block diagram showing the configuration of a receivingapparatus according to Embodiment 1 of the present invention;

FIG. 5 is an input/output relationship diagram of a conventionaltransmission power amplification section;

FIG. 6 is a drawing showing QPSK symbol and pilot symbol signal pointarrangement in the IQ plane according to Embodiment 1 of the presentinvention;

FIG. 7 is a drawing showing 16QAM symbol and pilot symbol signal pointarrangement in the IQ plane according to Embodiment 1 of the presentinvention;

FIG. 8 is an input/output relationship diagram of two kinds oftransmission power amplification sections according to Embodiment 1 ofthe present invention;

FIG. 9 is an input/output relationship diagram of a transmission poweramplification section according to Embodiment 1 of the presentinvention;

FIG. 10 is a graph of the power ratio of a QPSK modulation pilot symboland signal point according to Embodiment 1 of the present invention vs.the desired carrier power to noise power ratio necessary for bit errorrates of 10⁻⁴ and 10⁻⁶;

FIG. 11 is a block diagram showing the configuration of a transmittingapparatus that performs common amplification according to Embodiment 1of the present invention;

FIG. 12 is a drawing showing an example of the frame configuration of asignal transmitted by a communication terminal according to Embodiment 2of the present invention;

FIG. 13 is a block diagram showing the configuration of a receivingapparatus in a base station according to Embodiment 2 of the presentinvention;

FIG. 14 is a drawing showing an example of the frame configuration of asignal transmitted by a base station according to Embodiment 2 of thepresent invention;

FIG. 15 is a block diagram showing the configuration of the transmittingapparatus of a communication terminal according to Embodiment 2 of thepresent invention;

FIG. 16 is a block diagram showing the configuration of the receivingapparatus of a communication terminal according to Embodiment 2 of thepresent invention;

FIG. 17 is a drawing showing examples of the frame configurations ofsignals transmitted by a base station in the CDMA method according toEmbodiment 3 of the present invention;

FIG. 18 is a block diagram showing the configuration of the transmittingapparatus of a base station in the CDMA method according to Embodiment 3of the present invention;

FIG. 19 is a block diagram showing the configuration of the receivingapparatus of a base station in the CDMA method according to Embodiment 3of the present invention;

FIG. 20 is a drawing showing an example of the frame configuration of asignal transmitted by a communication terminal in the CDMA methodaccording to Embodiment 3 of the present invention;

FIG. 21 is a block diagram showing the configuration of the transmittingapparatus of a communication terminal in the CDMA method according toEmbodiment 3 of the present invention;

FIG. 22 is a block diagram showing the configuration of the receivingapparatus of a communication terminal in the CDMA method according toEmbodiment 3 of the present invention;

FIG. 23 is a block diagram showing the configuration of the receivingapparatus of a base station according to Embodiment 4 of the presentinvention;

FIG. 24 is a drawing showing an example of a frame configurationaccording to Embodiment 5 of the present invention;

FIG. 25 is a drawing showing QPSK symbol and pilot symbol signal pointarrangement in the IQ plane according to Embodiment 5 of the presentinvention;

FIG. 26 is a drawing showing 16QAM symbol and pilot symbol signal pointarrangement in the IQ plane according to Embodiment 5 of the presentinvention;

FIG. 27 is a drawing showing 64QAM symbol signal point arrangement inthe IQ plane according to Embodiment 5 of the present invention;

FIG. 28 is a drawing showing the configuration of a transmittingapparatus according to Embodiment 5 of the present invention;

FIG. 29 is a block diagram showing the configuration of a quadraturebaseband signal generating section according to Embodiment 5 of thepresent invention;

FIG. 30 is a drawing showing the configuration of a receiving apparatusaccording to Embodiment 5 of the present invention;

FIG. 31 is a drawing showing an example of the frame configuration of asignal transmitted by a base station according to Embodiment 6 of thepresent invention;

FIG. 32 is a block diagram showing the configuration of the transmittingapparatus of a base station according to Embodiment 6 of the presentinvention;

FIG. 33 is a block diagram showing the configuration of the receivingapparatus of a communication terminal according to Embodiment 6 of thepresent invention;

FIG. 34 is a block diagram showing the internal configuration of amodulation section according to Embodiment 6 of the present invention;

FIG. 35 is a block diagram showing the configuration of the transmittingapparatus of a base station according to Embodiment 6 of the presentinvention;

FIG. 36 is an input/output relationship diagram of a transmission poweramplification section according to Embodiment 7 of the presentinvention; and

FIG. 37 is a conceptual diagram showing the range in which communicationfrom a base station is possible for each modulation method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference now to the attached drawings, embodiments of the presentinvention will be explained in detail below.

Embodiment 1

FIG. 2 shows an example of a frame configuration according to thisembodiment. Modulation methods are explained below, taking a combinationof three kinds—QPSK, 16QAM, and 64QAM—as an example.

In FIG. 2, a preamble 101, pilot symbols 103, and a unique word 104, arecontrol information, and the preamble 101 includes information on theselected modulation method, including information indicating QPSK,16QAM, or 64QAM. Data symbols 102 contain data information. The pilotsymbols 103 are used to perform estimation of the radio wave propagationenvironment and coherent detection, and the unique word 104 is a signalfor having the receiving apparatus achieve time synchronization with thetransmitting apparatus. These items of control information require,greater reliability than data symbols.

FIG. 3 shows the configuration of a transmitting apparatus according tothis embodiment. In FIG. 3, in a QPSK signal generating section 201,when the modulation method information included in a control signalamong the input transmit digital signals and control signals is QPSK, aquadrature baseband signal is generated in accordance with the frameconfiguration in FIG. 2, the in-phase component of the QPSK quadraturebaseband signal is output to an in-phase component switching section204, and the quadrature phase component of the QPSK quadrature basebandsignal is output to a quadrature phase component switching section 205.

In a 16QAM signal generating section 202, when the modulation methodinformation included in a control signal among the input transmitdigital signals and control signals is 16QAM, a quadrature basebandsignal is generated in accordance with the frame configuration in FIG.2, the in-phase component of the 16QAM quadrature baseband signal isoutput to the in-phase component switching section 204, and thequadrature phase component of the 16QAM quadrature baseband signal isoutput to the quadrature phase component switching section 205.

In a 64QAM signal generating section 203, when the modulation methodinformation included in a control signal among the input transmitdigital signals and controls signals is 64QAM, a quadrature basebandsignal is generated in accordance with the frame configuration in FIG.2, the in-phase component of the 64QAM quadrature baseband signal isoutput to the in-phase component switching section 204, and thequadrature phase component of the 64QAM quadrature baseband signal isoutput to the quadrature phase component switching section 205.

The in-phase component switching section 204 switches the input part,based on the quadrature baseband signal in-phase component input by theQPSK signal generating section 201, 16QAM signal generating section 202,or 64QAM signal generating section 203, and modulation method intonationcontained in a control signal among control signals input according to aseparate rate, so that the quadrature baseband signal in-phase componentof the specified modulation method is input, and outputs the inputquadrature baseband signal in-phase component to a radio section 206.

The quadrature phase component switching section 205 switches the inputpart, based on the quadrature baseband signal in-phase component inputby the QPSK signal generating section 201, 16QAM signal generatingsection 202, or 64QAM signal generating section 203, and modulationmethod information contained in a control signal among control signalsinput according to a separate rate, so that the transmit quadraturebaseband signal quadrature phase component of the specified modulationmethod is input, and outputs the input quadrature base band signalquadrature phase component to the radio section 206.

The radio section 206 performs predetermined radio processing on thetransmit quadrature baseband signal in-phase component output from thein-phase component switching section 204 and the transmit quadraturebaseband signal quadrature phase component output from the quadraturephase component switching section 205, and outputs the result to atransmission power amplification section 207. The transmission poweramplification section 207 amplifies the signal that has undergone radioprocessing by the radio section 206, and transmits the amplifiedtransmit signal via a transmit antenna 208.

FIG. 4 shows the configuration of a receiving apparatus according tothis embodiment. In FIG. 4, a receive radio section 302 performspredetermined radio processing on a signal received via a receiveantenna 301 (received signal), and outputs the received quadraturebaseband signal in-phase component and received quadrature basebandsignal quadrature phase component to a synchronization/modulation methoddetermination section 303, fading distortion estimation section 304,frequency offset estimation section 305, QPSK detection section 306,16QAM detection section 307, and 64QAM detection section 308.

The synchronization/modulation method determination section 303 detectsthe unique word in FIG. 2 from the received quadrature baseband signalin-phase component and received quadrature baseband signal quadraturephase component output from the receive radio section 302, and achievestime synchronization with the transmitting apparatus based on thedetected unique word. In addition; the synchronization/modulation methoddetermination section 303 detects the preamble and identifies modulationmethod information contained in the preamble. A control signalcontaining these two items of information is output to the QPSKdetection section 306, 16QAM detection section 307, and 64QAM detectionsection 308.

The fading distortion estimation section 304 estimates distortion due tofading from the pilot symbol in FIG. 2 using the received quadraturebaseband signal in-phase component and received quadrature basebandsignal quadrature phase component output from the receive radio section302, and a control signal output from the synchronization/modulationmethod determination section 303, and outputs a fading distortionestimation signal to the QPSK detection section 306, 16QAM detectionsection 307, and 64QAM detection section 308.

The frequency offset estimation section 305 estimates the frequencyoffset from the pilot symbol in FIG. 2 using the received quadraturebaseband signal in-phase component and quadrature phase component outputfrom the receive radio section 302, and a control signal output from thesynchronization/modulation method determination section 303, and outputsa frequency offset estimation signal to the QPSK detection section 306,16QAM detection section 307, and 64QAM detection section 308.

When modulation method information contained in the control signaloutput from the synchronization/modulation method determination section303 indicates QPSK, the QPSK detection section 306 performs eliminationand demodulation of fading distortion and frequency offset in thereceived quadrature baseband signal in-phase component and receivedquadrature baseband signal quadrature phase component output from thereceive radio section 302, using the fading distortion estimation signaloutput from the fading distortion estimation section 304 and thefrequency offset estimation signal output from the frequency offsetestimation section 305, and outputs a QPSK received digital signal.

When modulation method information contained in the control signaloutput from the synchronization/modulation method determination section303 indicates 16QAM, the 16QAM detection section 307 performselimination and demodulation of fading distortion and frequency offsetin the received quadrature baseband signal in-phase component andreceived quadrature baseband signal quadrature phase component outputfrom the receive radio section 302, using the fading distortionestimation signal output from the fading distortion estimation section304 and the frequency offset estimation signal output from the frequencyoffset estimation section 305, and outputs a 16QAM received digitalsignal.

When modulation method information contained in the control signaloutput from the synchronization/modulation method determination section303 indicates 64QAM, the 64QAM detection section 308 performselimination and demodulation of fading distortion and frequency offsetin the received quadrature baseband signal in-phase component andreceived quadrature baseband signal quadrature phase component outputfrom the receive radio section 302, using the fading distortionestimation signal output from the fading distortion estimation section304 and the frequency offset estimation signal output from the frequencyoffset estimation section 305, and outputs a 64QAM received digitalsignal.

Next, the operation of a transmitting apparatus and receiving apparatusthat have the above-described configuration will be described. First,the transmit digital signal and control signal shown in FIG. 3 are inputto the QPSK signal generating section 201, 16QAM signal generatingsection 202, and 64QAM signal generating section 203, only the signalgenerating section that matches the modulation method information of thecontrol signal is operated, and by means of the signal generatingsection for the relevant modulation method, a quadrature baseband signalis generated, the quadrature baseband signal in-phase component isoutput to the in-phase component switching section 204, and thequadrature baseband signal quadrature phase component is output to thequadrature phase component switching section 205.

The quadrature baseband signal in-phase component output from themodulation method determination section is switched to the input sectioncorresponding to the modulation method indicated by the control signalby the in-phase component switching section 204, and is output to theradio section 206. Also, the quadrature baseband signal quadrature phasecomponent output from the modulation method determination section isswitched to the input section corresponding to the modulation methodindicated by the control signal by the quadrature phase componentswitching section 205, and is output to the radio section 206.

The transmit quadrature baseband signal in-phase component output fromthe in-phase component switching section 204 and the transmit quadraturebaseband signal quadrature phase component output from the quadraturephase component switching section 205 undergo predetermined radioprocessing by the radio section 206, and a transmit signal is output tothe transmission power amplification section 207. The transmit signaloutput from the radio section 206 undergoes power amplification by theamplification section 207, and is transmitted to the receiving apparatusvia the transmit antenna 208.

The signal transmitted by the transmitting apparatus is received by thereceiving apparatus via the antenna 301 shown in FIG. 4. In FIG. 4, thesignal received via the antenna 301 (received signal) undergoespredetermined radio processing by the receive radio section 302, and thereceived quadrature baseband signal in-phase component and receivedquadrature baseband signal quadrature phase component are output to thesynchronization/modulation method determination section 303, fadingdistortion estimation section 304, frequency offset estimation section305, QPSK detection section 306, 16QAM detection section 307, and 64QAMdetection section 308.

For the received quadrature baseband signal in-phase component andreceived quadrature baseband signal quadrature phase component outputfrom the receive radio section 302, the unique word shown in FIG. 2 isdetected by the synchronization/modulation method determination section303, and time synchronization with the transmitting apparatus isachieved based on the detected unique word. In addition, the preamble isdetected and modulation method information contained in the preamble isidentified. A control signal containing these two items of informationis generated, and is output to the fading distortion estimation section304, frequency offset estimation section 305, QPSK detection section306, 16QAM detection section 307, and 64QAM detection section 308.

For the received quadrature baseband signal in-phase component andreceived quadrature baseband signal quadrature phase component outputfrom the receive radio section 302, and a control signal output from thesynchronization/modulation method determination section 303, distortiondue to fading is estimated from the pilot symbol shown in FIG. 2 by thefading distortion estimation section 304, and a fading distortionestimation signal is output to the QPSK detection section 306, 16QAMdetection section 307, and 64QAM detection section 308.

Also, for the received quadrature baseband signal in-phase component andreceived quadrature baseband signal quadrature phase component outputfrom the receive radio section 302, and a control signal output from thesynchronization/modulation method determination section 303, a frequencyoffset is estimated from the pilot symbol shown in FIG. 2 by thefrequency offset estimation section 305, and a frequency offsetestimation signal is output to the QPSK detection section 306, 16QAMdetection section 307, and 64QAM detection section 308.

The detection section corresponding to the modulation method informationof the control signal output from the synchronization/modulation methoddetermination section 303—that is, the QPSK detection section 306, 16QAMdetection section 307, or 64QAM detection section 308—performselimination and demodulation of fading distortion and frequency offsetin the received quadrature baseband signal in-phase component andquadrature phase component output from the receive radio section 302,using the fading distortion estimation signal output from the fadingdistortion estimation section 304 and the frequency offset estimationsignal output from the frequency offset estimation section 305, andoutputs a received digital signal according to the respective modulationmethod.

The operation of a transmission power amplification section in a radiocommunication system of this embodiment, and pilot symbol signal pointarrangement in each modulation method, will now be described. In thisembodiment, the pilot symbol signal point amplitude indicatestransmission power in the IQ plane, and when transmission power israised the pilot symbol signal point amplitude increases.

FIG. 5 shows the input/output relationship of a conventionaltransmission power amplification section. In FIG. 5, reference code 401denotes the operation point of the transmission power amplificationsection, indicating the average transmission output power. Referencecode 402, reference code 403, and reference code 404 denote the QPSK,16QAM, and 64QAM operating ranges (level ranges in which input of asignal to be input to the power amplification section is possible),respectively, and show the transmission power amplification sectionoperating range when the respective modulation method is selected. Asshown in FIG. 5, the operating range is greatest when the modulationmethod is 64QAM. Thus, conventionally, the operating range is determinedby the modulation method.

However, since the transmission power amplification section uses atransmission power amplifier capable of linear amplification of a 16QAMmodulation method signal, when the modulation method is QPSK or 16QAM,linear amplification is possible even if the operating range is extendedwithin a range in which the operating range does not exceed the 64QAMoperating range.

Thus, with a radio communication method that performs adaptivemodulation according to this embodiment, a method is used whereby pilotsymbol signal points are arranged in the IQ plane so that the receptionsensitivity characteristics of the receiving apparatus are most improvedwithin a range in which the greatest operating range of the transmissionpower amplifier does not exceed a wide modulation method operatingrange. That is to say, when the modulation method is QPSK or 16QAM, thepilot symbol input level is increased in a range in which the operatingrange does not exceed the 64QAM operating range, and the receptionsensitivity characteristics of the receiving apparatus are improved.This method will be described below.

FIG. 6 shows QPSK symbol and pilot symbol signal point arrangement inthe IQ plane according to this embodiment. Reference code 501 denotes aQPSK modulation signal point and reference code 502 denotes the pilotsymbol signal point. If the pilot symbol signal point amplification isdesignated r_(pilot), as r_(pilot) is increased resistance to pilotsymbol noise is strengthened in the receiving apparatus, the accuracy offading distortion estimation by the fading distortion estimation section304 and the accuracy of estimation by the frequency offset estimationsection 305 in the receiving apparatus in FIG. 4 is improved, andhigh-precision detection processing can be carried out, with the resultthat the reception sensitivity characteristics of the receivingapparatus are improved.

Further, FIG. 7 shows 16QAM symbol and pilot symbol signal pointarrangement in the IQ plane according to this embodiment. Reference code601 denotes a 16QAM signal point and reference code 602 denotes thepilot symbol signal point. If the pilot symbol signal pointamplification is designated r_(pilot), as r_(pilot) is increasedresistance to pilot symbol noise is strengthened in the receivingapparatus, the accuracy of fading distortion estimation by the fadingdistortion estimation section 304 and the accuracy of estimation by thefrequency offset estimation section 305 in the receiving apparatus inFIG. 4 is improved, and high-precision detection processing can becarried out, with the result that the reception sensitivitycharacteristics of the receiving apparatus are improved. The same alsoapplies to 64QAM.

Next, the operating ranges of two kinds of transmission poweramplification sections with different input/output characteristics willbe described. FIG. 8 shows the input/output relationship of two kinds oftransmission power amplification sections according to this embodiment.In order to attempt a general description, the two kinds of transmissionpower amplification sections are here designated transmission poweramplification section A and transmission power amplification section B.In FIG. 8, reference code 701 indicates the input/output relationship oftransmission power amplification section A, and reference code 702indicates the input/output relationship of transmission poweramplification section B. When the input level is in the operating rangeindicated by reference code 703, it can be handled by eithertransmission power amplification section A or transmission poweramplification section B. However, when the input level is in theoperating range indicated by reference code 704, there is a range thatcannot be handled by transmission power amplification section A. Forexample, to consider a communication apparatus for which use of amodulation method up to 16QAM is sufficient, assuming that input can behandled by use of a transmission power amplifier that has theinput/output characteristic indicated by reference code 701, powerconsumption can be kept lower than when using a transmission poweramplifier that has the input/output characteristic indicated byreference code 702. However, assuming that a transmission poweramplifier indicated by reference code 702 must be used in order tohandle 64QAM used in this embodiment, it is possible to secure a wideroperating range than the operating range indicated by reference code703. That is to say, when a QPSK or 16QAM modulation method is used, ifthe pilot symbol transmission power is increased in the operating rangeindicated by reference code 704, the accuracy of fading distortionestimation and frequency offset estimation in the receiving apparatusincreases, and the reception sensitivity characteristics of thereceiving apparatus improve.

In this embodiment, the greatest operating range of the transmissionpower amplification section is the 64QAM operating range. Therefore, asa result of making r_(pilot) larger than r_(QPSK), the operating rangein the transmission power amplification section is increased; but aslong as the range is within the 64QAM method operating range,amplification is still possible when QPSK is selected. The same can beassumed when 16QAM is used.

Taking the above into consideration, it becomes possible to arrive atthe kind of transmission power amplification section input/outputrelationship shown in FIG. 9. FIG. 9 is a graph showing the input/outputrelationship of a transmission power amplification section according tothis embodiment, in which reference code 801 denotes the operation pointof the transmission power amplification section, reference code 802denotes the QPSK operating range when the pilot symbol signal pointamplitude is made greater than the maximum signal point amplitude inconventional QPSK modulation, reference code 803 denotes the 16QAMoperating range when the pilot symbol signal point amplitude is madegreater than the 16QAM maximum signal point amplitude, and referencecode 804 denotes the 64QAM method operating range. Note that theoperating range denoted by reference code 802 and the operating rangedenoted by reference code 803 are taken to be smaller than the 64QAMoperating range. At this time, the QPSK operating range and 16QAMoperating range in FIG. 9 are greater than when a transmission poweramplification section is used as shown in FIG. 5, but amplification ispossible and it is also possible to set the operating range of eachmodulation method as the same range. Meanwhile, in the receivingapparatus, when QPSK or 16QAM is used, resistance to pilot symbol noiseis strengthened. However, it is not necessarily the case that the pilotsymbol amplitude need only be increased, and the fact that there is anoptimum amplitude will now be explained using FIG. 10.

FIG. 10 shows a graph of the power ratio of a QPSK modulation pilotsymbol and signal point according to this embodiment vs. the desiredcarrier power to noise power ratio necessary for bit error rates of 10⁻⁴and 10⁻⁶. Reference code 901 indicates the desired carrier power tonoise power ratio necessary for a bit error rate of 10⁻⁴, and referencecode 902 indicates the desired carrier power to noise power rationecessary for a bit error rate of 10⁻⁶. Looking at reference code 901,on the horizontal axis of lowest values of the desired carrier power tonoise power ratio at a bit error rate of 10⁻⁴ (r² _(pilot)/r² _(QPSK)),the value is 2, and it is not the case that the desired carrier power tonoise power ratio decreases even though the pilot signal amplitudeincreases. The same can be assumed in the case of a 10⁻⁶ bit error rateindicated by reference code 902, and it can be said that there is anoptimum amplitude of the pilot signal.

With this embodiment, the description has been based on a single carriermethod, but implementation is also possible in a similar way with amultiplexing method, CDMA method, or OFDM (Orthogonal Frequency DivisionMultiplexing) method.

The fact that this embodiment can also be applied in commonamplification will now be explained below using FIG. 11. FIG. 11 showsthe configuration of a transmitting apparatus that performs commonamplification according to this embodiment. An f1 modulation section1001 performs digital modulation of a frequency f1 digital signal, andoutputs a frequency f1 transmit signal to an adding section 1004. An f2modulation section 1002 performs digital modulation of a frequency f2digital signal, and outputs a frequency f2 transmit signal to the addingsection 1004. An fn modulation section 1003 performs digital modulationof a frequency fn digital signal, and outputs a frequency fn transmitsignal to the adding section 1004.

The adding section 1004 adds the frequency f1 transmit signal, frequencyf2 transmit signal, and frequency fn transmit signal, and outputs thetransmit signal resulting from the addition to a transmission poweramplification section 1005. The transmission power amplification section1005 amplifies the transmit signal resulting from the addition andtransmits the amplified transmit signal via a transmit antenna 1006.

According to the above-described embodiment, with a radio communicationmethod that performs adaptive modulation, the reception sensitivitycharacteristics of a receiving apparatus can be improved by placing thepilot symbol signal point in the IQ plane so that the receptionsensitivity of the receiving apparatus is made optimal, whilemaintaining the average transmission output power of the transmittingapparatus at a fixed level.

A combination of three kinds of modulation methods—QPSK, 16QAM, and64QAM—has been taken as an example in the description, but thisembodiment is not limited to these modulation methods, and moreover isnot limited to switching between three modulation methods.

In this embodiment, a known signal point has been taken as an examplefor the pilot symbol in the description, but this is not a limitation,and a PSK modulation signal, for example, may also be used as a pilotsymbol.

Also, in this embodiment, a pilot symbol is used in fading distortionestimation and frequency offset estimation in the receiving apparatus,but these can also be performed using other control information such asa preamble or unique word as shown in FIG. 2.

As regards control information, also, of which channel controlinformation with data eliminated is an example, the same kind ofimplementation is possible as for a pilot symbol in this embodiment. Atthis time, control information is characterized in having greater errortolerance for noise compared with data in particular.

Embodiment 2

In Embodiment 2, a communication system modulation method determinationmethod will be described whereby the modulation method is switchedaccording to the radio wave propagation environment and thecommunication traffic in a radio communication system, transmittingapparatus, and receiving apparatus using the method described inEmbodiment 1.

FIG. 12 is a drawing showing an example of the frame configurationtransmitted by a communication terminal according to this embodiment.The parts in FIG. 12 identical to those in FIG. 2 are assigned the samecodes as in FIG. 2 and their detailed explanations are omitted. In FIG.12, reference code 1101 denotes a preamble, containing controlinformation. Reference code 1102 denotes radio wave propagationenvironment estimation information, being symbols whereby acommunication terminal estimates the radio wave propagation environmentof a signal transmitted by the base station, for notification to thebase station as radio wave propagation environment information.

Next the configuration of a base station receiving apparatus will bedescribed. FIG. 13 shows the configuration of a base station receivingapparatus according to this embodiment. In FIG. 13, a receive radiosection 1202 performs predetermined radio processing on a signalreceived via an antenna 1201 (received signal), and outputs the receivedquadrature baseband signal in-phase component and received quadraturebaseband signal quadrature phase component to a synchronization section1203 and detection section 1204.

The synchronization section 1203 detects the 304 unique word in FIG. 12from the received quadrature baseband in-phase component and receivedquadrature baseband signal quadrature phase component output from thereceive radio section 1202, achieves time synchronization with thecommunication terminal based on the detected unique word, and outputs asignal as a synchronization signal to the detection section 1204.

The detection section 1204 performs detection processing on a signaltransmitted from the communication terminal according to the receivedquadrature baseband signal in-phase component and received quadraturebaseband signal quadrature phase component output from the receive radiosection 1202, and the synchronization signal output from thesynchronization section 1203, and outputs a received digital signal to adata detection section 1205.

The data detection section 1205 outputs radio wave propagationenvironment information to a transmit data generating section 1206 fromthe received digital signal output from the detection section 1204 basedon the frame configuration in FIG. 11, and outputs receive data.

The transmit data generating section 1206 determines the modulationmethod based on the radio wave propagation environment information fromwithin the radio wave propagation environment information output fromthe data detection section 1205 and the input transmit data, and outputsa transmit digital signal that has information bits corresponding to thedetermined modulation method and a control signal notifying the basestation of the determined modulation method. If it is determined by thedata detection section 1205 that there is a plurality of arriving waves,other parameters indicating the radio wave propagation environment haveno effect, and the transmit data generating section 1206 selects QPSK,which has good error tolerance, and issues a request to thecommunication terminal. This is done to prevent the reception of aplurality of arriving waves, since the receiving apparatus cannotperform signal demodulation in such a case.

FIG. 14 shows an example of the frame configuration transmitted by abase station according to this embodiment. The parts in FIG. 14identical to those in FIG. 12 are assigned the same codes as in FIG. 12and their detailed explanations are omitted. In FIG. 14, reference code1301 denotes modulation method information, being symbols for notifyingthe communication terminal of the modulation method of the base station.

Next, the configuration of the transmitting apparatus of a communicationterminal apparatus will be described. FIG. 15 shows the configuration ofthe transmitting apparatus of a communication terminal according to thisembodiment. In FIG. 15, a transmit data generating section 1401generates a transmit digital signal in accordance with the frameconfiguration in FIG. 12 from transmit data and a radio wave propagationenvironment estimation signal, and outputs it to a quadrature basebandsignal generating section 1402.

The quadrature baseband signal generating section 1402 generates atransmit quadrature baseband signal in-phase component and transmitquadrature baseband signal quadrature phase component from the transmitdigital signal output from the transmit data generating section 1401,and outputs them to a transmit radio section 1403.

The transmit radio section 1403 performs predetermined radio processingon the transmit quadrature baseband signal in-phase component andtransmit quadrature baseband signal quadrature phase component generatedby the quadrature baseband signal generating section 1402, and outputs atransmit signal to a transmission power amplification section 1404. Thetransmission power amplification section 1404 amplifies the transmitsignal output from the transmit radio section 1403 and outputs theamplified transmit signal to the base station via a transmit antenna1405.

FIG. 16 shows the configuration of the receiving apparatus of acommunication terminal according to this embodiment. In FIG. 16, areceive radio section 1502 performs predetermined radio receptionprocessing on a signal received via a receive antenna 1501 (receivedsignal), and outputs the received quadrature baseband signal in-phasecomponent and received quadrature baseband signal quadrature phasecomponent.

A synchronization/modulation method determination section 1506 detectsthe unique word 104 of the frame configuration transmitted by the basestation in FIG. 14 from the received quadrature baseband signal in-phasecomponent and received quadrature baseband signal quadrature phasecomponent output from the receive radio section 1502 and achieves timesynchronization with the base station, and also detects modulationmethod information 1301, estimates the modulation method, and outputs asynchronization signal and modulation method information to eachmodulation method detection section.

If modulation method information indicates QPSK based on the receivedquadrature baseband signal in-phase component and received quadraturebaseband signal, synchronization signal, and modulation methodinformation, the QPSK detection section 1503 performs demodulation andoutputs a QPSK-detected received digital signal.

If modulation method information indicates 16QAM based on the receivedquadrature baseband signal in-phase component and received quadraturebaseband signal, synchronization signal, and modulation methodinformation, the 16QAM detection section 1504 performs demodulation andoutputs a 16QAM-detected received digital signal.

If modulation method information indicates 64QAM based on the receivedquadrature baseband signal in-phase component and received quadraturebaseband signal, synchronization signal, and modulation methodinformation, the 64QAM detection section 1505 performs demodulation andoutputs a 64QAM-detected received digital signal.

An interference wave strength estimation section 1507 estimatesinterference wave strength from a modulation signal, unique word, orpilot symbol in the received quadrature baseband signal in-phasecomponent and received quadrature baseband signal quadrature phasecomponent output from the receive radio section 1502, and outputs aninterference wave strength estimation signal to a radio wave propagationenvironment estimation section 1511.

A field strength estimation section 1508 estimates the reception fieldstrength or carrier power to noise power ratio from a modulation signal,unique word, or pilot symbol in the received quadrature baseband signalin-phase component and received quadrature baseband signal quadraturephase component output from the receive radio section 1502, and outputsa field strength estimation signal to the radio wave propagationenvironment estimation section 1511.

A multipath estimation section 1509 estimates the multipath situationfrom a modulation signal, unique word, or pilot symbol in the receivedquadrature baseband signal in-phase component and received quadraturebaseband signal quadrature phase component output from the receive radiosection 1502, and outputs a multipath estimation signal to the radiowave propagation environment estimation section 1511.

A Doppler frequency estimation section 1510 estimates the Dopplerfrequency from a modulation signal, unique word, or pilot symbol in thereceived quadrature baseband signal in-phase component and receivedquadrature baseband signal quadrature phase component output from thereceive radio section 1502, and outputs a Doppler frequency estimationsignal to the radio wave propagation environment estimation section1511.

The radio wave propagation environment estimation section 1511determines and outputs the modulation method to be requested of the basestation from the interference wave strength estimation signal, fieldstrength estimation signal, multipath estimation signal, and Dopplerfrequency estimation signal, so that, for example, QPSK is selected whenthe field strength is weak, when the Doppler frequently is large, whenthere is a plurality of arriving waves, or when the interference wavestrength is great. If it is determined by the multipath estimationsection 1509 that there is a plurality of arriving waves, otherparameters indicating the radio wave propagation environment have noeffect, and the radio wave propagation environment estimation section1511 selects a modulation method with good error tolerance (in thisembodiment, QPSK), and issues a request to the communication terminalaccordingly. Alternatively, the radio wave propagation environmentestimation section 1511 may output the interference wave strengthestimation signal, field strength estimation signal, multipathestimation signal, and Doppler frequency estimation signal themselves.This is done to prevent the reception of a plurality of arriving waves,since the receiving apparatus cannot perform signal demodulation in sucha case.

Next, the operation of a base station and communication terminal thathave the above-described configurations will be described. First, in thecommunication terminal transmitting apparatus shown in FIG. 15, transmitdata and a radio wave propagation environment estimation signal aregenerated as a transmit digital signal in accordance with the frameconfiguration in FIG. 12 by the transmit data generating section 1401,and output to the quadrature baseband signal generating section 1402.

The transmit digital signal output from the transmit data generatingsection 1401 is generated as a transmit quadrature baseband signalin-phase component and transmit quadrature baseband signal quadraturephase component by the quadrature baseband signal generating section1402, and output to the transmit radio section 1403.

The transmit quadrature baseband signal in-phase component and transmitquadrature baseband signal quadrature phase component output from thequadrature baseband signal generating section 1402 undergo predeterminedradio processing by the transmit radio section 1403, and a transmitsignal is output to the transmission power amplification section 1404.

The transmit signal on which predetermined radio processing has beenperformed by the transmit radio section undergoes power amplification bythe transmission power amplification section 1404 and is transmitted viathe transmit antenna 1405.

The signal transmitted by the communication terminal is received by thebase station shown in FIG. 13. In FIG. 13, the signal received via thereceive antenna 1201 (received signal) undergoes predetermined radioprocessing by the receive radio section 1202, and the receivedquadrature baseband signal in-phase component and received quadraturebaseband signal quadrature phase component are output to thesynchronization section 1203 and detection section 1204.

For the received quadrature baseband signal in-phase component andreceived quadrature baseband signal quadrature phase component outputfrom the receive radio section 1202, a unique word is detected by thesynchronization section 1203, time synchronization with thecommunication terminal is achieved based on the detected unique word,and a synchronization signal is generated and output to the detectionsection 1204.

The received quadrature baseband signal in-phase component and receivedquadrature baseband signal quadrature phase component output from thereceive radio section 1202 undergo detection processing by the detectionsection 1204 based on the synchronization signal output from thesynchronization section 1203, and a received digital signal is output tothe data detection section 1205.

For the received digital signal output from the detection section 1204,radio wave propagation environment information is generated by the datadetection section 1205, and is output to the transmit data generatingsection 1206. In addition, receive data is output.

With regard to the radio wave propagation environment information outputfrom the data detection section 1205, the modulation method isdetermined by the transmit data generating section 1206 according to theradio wave propagation environment so that, for example, QPSK isselected when the field strength is weak, when the Doppler frequency islarge, when there is a plurality of arriving waves, or when theinterference wave strength is great, then the transmit data is modulatedusing that modulation method, and a transmit digital signal is output.In addition, a control signal modulated using the determined modulationmethod is output.

Next, the signal transmitted from the base station transmittingapparatus (see FIG. 2) is received by the communication terminalreceiving apparatus shown in FIG. 16. In FIG. 16, the signal receivedvia the receive antenna 1501 (received signal) undergoes predeterminedreception processing by the receive radio section 1502, and the receivedquadrature baseband signal in-phase component and received quadraturebaseband signal quadrature phase component are output to theinterference wave strength estimation section 1507, field strengthestimation section 1508, multipath estimation section 1509, Dopplerfrequency estimation section 1510, QPSK detection section 1503, 16QAMdetection section 1504, 64QAM detection section 1505, andsynchronization/modulation method determination section 1506.

For the received quadrature baseband signal in-phase component andreceived quadrature baseband signal quadrature phase component outputfrom the receive radio section 1502, a unique word is detected by thesynchronization/modulation method determination section 1506, and timesynchronization with the base station is achieved based on the detectedunique word. In addition, modulation method information is detected, themodulation method is estimated, and a synchronization signal andmodulation method information are output to each modulation methoddetection section.

The received quadrature baseband signal in-phase component and receivedquadrature baseband signal quadrature phase component output from thereceive radio section 1502 are demodulated in a modulation methoddetection section based on the synchronization signal and modulationmethod information output from the synchronization/modulation methoddetermination section 1506, and a corresponding received digital signalis output.

For the received quadrature baseband signal in-phase component andreceived quadrature baseband signal quadrature phase component outputfrom the receive radio section 1502, parameters for estimating thepropagation environment are estimated in each estimation section, and anestimation signal is output to the radio wave propagation environmentestimation section 1511.

For the estimation signal output from each estimation section, the radiowave propagation environment is determined as a whole by the radio wavepropagation environment estimation section 1511, and radio wavepropagation environment information to be reported to the base stationis estimated and output.

Next, an explanation will be given concerning the modulation methodselected initially for a transmit signal to be transmitted by a basestation. When a radio communication system of the kind described in thisembodiment is constructed, for example, the modulation method to be usedinitially for a signal to be transmitted by the base station presents aproblem. In this case, since a signal has not once been transmitted tothe communication terminal, the communication terminal cannot estimatethe radio wave propagation environment. Therefore, the base station mustitself decide the modulation method to be used initially. If, forexample, 16QAM or 64QAM is used as the initial modulation method, acommunication terminal will not be able to attain data quality when theradio wave propagation environment is poor. Taking this fact intoconsideration, it is preferable to select QPSK modulation.

By selecting the most noise tolerant of the switchable modulationmethods as the initially selected modulation method, as described above,data quality is improved at the communication terminal. This initialsetting of the modulation method is not limited to this embodiment, andcan be applied to communication methods characterized by switching ofthe modulation method according to the radio wave propagationenvironment, communication traffic, and so forth.

Similarly, with a communication method characterized by changing of theerror correction method according to the radio wave propagationenvironment, the same kind of approach can be taken to the initial errorcorrection method for a transmit signal to be transmitted. By selectingthe error correction method with the greatest error correctioncapability from among the switchable error correction methods as theinitially selected error correction method, data quality is improved.This initial setting of the error correction method is not limited tothis embodiment, and can be applied to communication methodscharacterized by switching of the error correction method according tothe radio wave propagation environment, communication traffic, and soforth.

If the modulation method is variable, the preamble 101 excluding datasymbols 102, the unique word 104, and the pilot symbol 103 in FIG. 14are constantly transmitted. Using these signals transmitted by the basestation, a communication terminal estimates the radio wave propagationenvironment and in starting communication with the base stationtransmits radio wave propagation environment information to the basestation, and the base station determines the initial modulation methodfor the data symbols 102 based on the radio wave propagation environmentinformation transmitted from the communication terminal, therebyenabling data quality to be attained. At this time, modulation methodinformation can also be included in the radio wave propagationenvironment information. Initial setting of the modulation method bythis method is not limited to this embodiment, and can be applied tocommunication methods characterized by switching of the modulationmethod according to the radio wave propagation environment,communication traffic, and so forth. Also, while the preamble, uniqueword, and pilot symbol have been described as constantly transmittedsignals, this is not a limitation, and special symbols for radio wavepropagation environment estimation may also be inserted.

Similarly, with a communication method characterized by changing of theerror correction method according to the radio wave propagationenvironment, for example, the same kind of approach can be taken to theerror correction method for initial transmission. Having thecommunication terminal estimate the radio wave propagation environmentfrom the signals constantly transmitted by the base station, and havingthe base station decide on the data symbol error correction method basedon radio wave propagation environment information transmitted from thecommunication terminal, enables data quality to be attained. At thistime, error correction method information can also be included in theradio wave propagation environment information. Initial setting of themodulation method by this method is not limited to this embodiment, andcan be applied to communication methods characterized by switching ofthe modulation method according to the radio wave propagationenvironment, communication traffic, and so forth.

By means of the above, it is possible to configure a radio communicationsystem, transmitting apparatus, and receiving apparatus that use themethod described in Embodiment 1, and by this means, it is possible toimprove the reception sensitivity characteristics of a receivingapparatus. In this case, the description has referred to a combinationof three kinds of modulation methods—QPSK, 16QAM, and 64QAM—but thisembodiment is not limited to this, and neither is it limited toswitching between three kinds of modulation methods. Moreover, in FIG. 3and FIG. 13 it is also possible to input communication trafficinformation, for example, and to consider this in deciding on themodulation method. Furthermore, interference wave strength, fieldstrength, the multipath situation, and Doppler frequency have beendescribed as radio wave propagation environment parameters by way ofexamples, but this embodiment is not limited to these.

Embodiment 3

In Embodiment 3, initial settings and a setting method are described fora case where the modulation method of each channel is changed adaptivelyaccording to the radio wave propagation environment, communicationtraffic, and so forth, in the CDMA method. At this time, a communicationmethod is used whereby the base station primary modulation (datamodulation) can be switched between QPSK modulation, 16QAM, and 64QAM,according to the radio wave propagation environment, communicationtraffic, and so forth.

FIG. 17 shows examples of the frame configurations of signalstransmitted by a base station in the CDMA method according to thisembodiment. The control channel frame is composed of channel Amodulation method information 1601, channel A transmission power controlinformation 1602, channel Z modulation method information 1603, andchannel Z transmission power control information 1604. The channel Aframe configuration comprises channel A data symbols 1605, and the QPSK,16QAM, or 64QAM modulation method is used for primary modulation ofchannel A data symbols 1605. The channel Z frame configuration compriseschannel Z data symbols 1606, and the QPSK, 16QAM, or 64QAM modulationmethod is used for primary modulation of channel Z data symbols 1606.

FIG. 18 shows the configuration of the transmitting apparatus of a basestation in the CDMA method according to this embodiment. A channel Aspread spectrum modulation section 1701 performs QPSK modulation, 16QAM,or 64QAM primary modulation on a channel A transmit digital signal basedon channel A modulation method information in the input channel Atransmit digital signal and channel A modulation method information, andoutputs a channel A transmit quadrature baseband signal to an addingsection 1703.

A channel Z spread spectrum modulation section 1702 performs QPSKmodulation, 16QAM, or 64QAM primary modulation on a channel Z transmitdigital signal based on channel Z modulation method information in theinput channel Z transmit digital signal and channel Z modulation methodinformation, and outputs a channel Z transmit quadrature baseband signalto the adding section 1703.

The adding section 1703 adds the input pilot channel transmit quadraturebaseband signal, the control channel transmit quadrature basebandsignal, the transmit quadrature baseband signal output from the channelA spread spectrum modulation section 1701, and the transmit quadraturebaseband signal output from the channel Z spread spectrum modulationsection 1702, and outputs the transmit quadrature baseband signalresulting from this addition to a transmit radio section 1704.

The transmit radio section 1704 performs predetermined radio processingon the post-addition transmit quadrature baseband signal output from theadding section 1703, and outputs a transmit signal.

A transmission power amplification section 1705 amplifies the transmitsignal output from the transmit radio section 1704, and outputs theamplified transmit signal via an antenna 1706.

FIG. 19 shows the configuration of the receiving apparatus of a basestation in the CDMA method according to this embodiment. A receive radiosection 1802 performs predetermined radio processing on a signalreceived via an antenna 1801 (received signal), and outputs a receivedquadrature baseband signal to a channel A detection section 1803 andchannel Z detection section 1804.

The channel A detection section 1803 performs detection processing onthe received quadrature baseband signal output from the receive radiosection 1802, and outputs a channel A received digital signal to achannel A data detection section 1805. Similarly, the channel Zdetection section 1804 performs detection processing on the receivedquadrature baseband signal output from the receive radio section 1802,and outputs a channel Z received digital signal to a channel Z datadetection section 1806.

The channel A data detection section 1805 generates radio wavepropagation environment information estimated by the channel Acommunication terminal from the channel A received digital signal outputfrom the channel A detection section 1803, and outputs it to a channel Amodulation method determination section 1807.

The channel Z data detection section 1806 generates radio wavepropagation environment information estimated by the channel Zcommunication terminal from the channel Z received digital signal outputfrom the channel Z detection section 1804, and outputs it to a channel Zmodulation method determination section 1808.

The channel A modulation method determination section 1807 selects amodulation method that offers both channel A communication terminal dataquality and data transmission speed from among QPSK, 16QAM, and 64QAM,based on channel A radio wave propagation environment information outputfrom the channel A data detection section 1805, and outputs this to acontrol channel transmit signal generating section 1809 as channel Amodulation method information.

The channel Z modulation method determination section 1808 selects amodulation method that offers both channel Z communication terminal dataquality and data transmission speed from among QPSK, 16QAM, and 64QAM,based on channel Z radio wave propagation environment information outputfrom the channel Z data detection section 1806, and outputs this to thecontrol channel transmit signal generating section 1809 as channel Zmodulation method information.

Using channel A modulation method information output from the channel Amodulation method determination section 1807 and channel Z modulationmethod information output from the channel Z modulation methoddetermination section 1808, the control channel transmit signalgenerating section 1809 generates and outputs a control channel signalbased on the control channel frame configuration in FIG. 17 containingchannel A modulation method information and channel Z modulation methodinformation.

FIG. 20 shows an example of the frame configuration of a signaltransmitted by a communication terminal in the CDMA method according tothis embodiment. Reference code 1901 denotes radio wave propagationenvironment estimation information, whereby a communication terminalestimates the radio wave propagation environment of a signal transmittedby the base station, for notification to the base station. Referencecode 1902 denotes data symbols.

FIG. 21 shows the configuration of the transmitting apparatus of acommunication terminal in the CDMA method according to this embodiment.A transmit data generating section 2001 generates a transmit digitalsignal from the input transmit data and radio wave propagationenvironment estimation signal, and outputs it to a spread spectrummodulation section 2002.

The spread spectrum modulation section 2002 performs spectrum spreadingof the transmit digital signal output from the transmit data generatingsection 2001, and outputs a transmit quadrature baseband signal inaccordance with the frame configuration in FIG. 24 to a transmit radiosection 2003.

The transmit radio section 2003 performs predetermined radio processingon the transmit quadrature baseband signal output from the spreadspectrum modulation section 2002, and outputs a transmit signal to atransmission power amplification section 2004.

The transmission power amplification section 2004 amplifies the transmitsignal output from the transmit radio section 2003, and outputs theamplified transmit signal via an antenna 2005.

FIG. 22 shows the configuration of the receiving apparatus of acommunication terminal in the CDMA method according to this embodiment.In FIG. 22, a signal received via an antenna 2101 (received signal)undergoes predetermined reception processing by a receive radio section2102, and a received quadrature baseband signal in-phase component andreceived quadrature baseband signal quadrature phase component areoutput to a detection section 2103, interference wave strengthestimation section 2104, field strength estimation section 2105,multipath estimation section 2106, and Doppler frequency estimationsection 2107.

The detection section 2103 performs detection processing on the receivedquadrature baseband signal in-phase component and received quadraturebaseband signal quadrature phase component output from the receive radiosection 2102, and outputs the resulting signal.

The interference wave strength estimation section 2104 estimates theinterference wave strength from the pilot channel component and controlchannel component in the received quadrature baseband signal in-phasecomponent and received quadrature baseband signal quadrature phasecomponent output from the receive radio section 2102, and outputs aninterference wave strength estimation signal to a radio wave propagationenvironment estimation section 2108.

The field strength estimation section 2105 estimates the reception fieldstrength from the pilot channel component and control channel componentin the received quadrature baseband signal in-phase component andreceived quadrature baseband signal quadrature phase component outputfrom the receive radio section 2102, and outputs a field strengthestimation signal to the radio wave propagation environment estimationsection 2108.

The multipath estimation section 2106 estimates the multipath situationfrom the pilot channel component and control channel component in thereceived quadrature baseband signal in-phase component and receivedquadrature baseband signal quadrature phase component output from thereceive radio section 2102, and outputs a multipath estimation signal tothe radio wave propagation environment estimation section 2108.

The Doppler frequency estimation section 2107 estimates the Dopplerfrequency from the pilot channel component and control channel componentin the received quadrature baseband signal in-phase component andreceived quadrature baseband signal quadrature phase component outputfrom the receive radio section 2102, and outputs a Doppler frequencyestimation signal to the radio wave propagation environment estimationsection 2108.

By inserting modulation method information transmitted by the basestation into the control channel, as described above, it is possible forthe base station to send the modulation method of the transmit signalbeing transmitted to a communication terminal. Also, in particular, byhaving a communication terminal employ a method whereby the radio wavepropagation environment is estimated using a pilot channel and controlchannel transmitted by the base station, it is possible for thecommunication terminal to estimate the radio wave propagationenvironment even when the base station is not transmitting data symbolsto the communication terminal.

By adopting the above-described means, it is possible to achieve a radiocommunication system configuration whereby the modulation method of eachchannel is switched adaptively according to the radio wave propagationenvironment, communication traffic, and so forth, in the CDMA method.Similarly, it is possible to configure a radio communication systemwhereby the error correction method of each channel is variableaccording to the radio wave propagation environment, communicationtraffic, and so forth.

Next, a description will be given of the initial setting method for themodulation method when the modulation method of each channel is variableaccording to the radio wave propagation environment, communicationtraffic, and so forth, in the CDMA method. When a radio communicationsystem of the kind described in this embodiment is constructed, forexample, the modulation method to be used initially for a transmitsignal to be transmitted by the base station presents a problem. In thiscase, if, for example, 16QAM or 64QAM is used as the initial modulationmethod, a communication terminal will not be able to attain data qualitywhen the radio wave propagation environment is poor. Taking this factinto consideration, it is preferable to select QPSK modulation.

By selecting the most noise tolerant of the switchable modulationmethods as the initially selected modulation method, as described above,data quality is improved at the communication terminal.

Similarly, with a communication method whereby the error correctionmethod of each channel is variable according to the radio wavepropagation environment, communication traffic, and so forth, forexample, the same kind of approach can be taken to the error correctionmethod for initial transmission. By selecting the error correctionmethod with the greatest error correction capability from among theswitchable error correction methods as the initially selected errorcorrection method, data quality is improved.

The initial setting method will now be described for a case where themodulation method of each channel is switched according to the radiowave propagation environment, communication traffic, and so forth, inthe CDMA method. With this method, a communication terminal estimatesthe radio wave propagation environment from the signals the base stationtransmits constantly, for example, pilot channel and control channelsignals even when the communication terminal is not performing datacommunication with the base station. Then, when starting datacommunication with the base station, the communication terminal firsttransmits radio wave propagation environment information estimated fromthe pilot channel and control channel signals to the base station, andafter the base station receives this radio wave propagation environmentinformation, the base station makes a decision so that, for example,QPSK is selected as the modulation method of the signal to betransmitted when the field strength is weak, when the Doppler frequencyis large, when there is a plurality of arriving waves, or when theinterference wave strength is great. By means of the above, the qualityof the initial data transmitted by the base station is improved at thecommunication terminal.

Similarly, implementation is also possible in a communication systemwhereby the error correction method for the modulation method of eachchannel is variable according to the radio wave propagation environment,communication traffic, and so forth. A communication terminal estimatesthe radio wave propagation environment information estimated from thepilot channel and control channel constantly transmitted by the basestation, and when starting communication with the base station,transmits radio wave propagation environment information to the basestation, which decides on the data symbol error correction method sothat, for example, a method with good error correction capability isselected when the field strength is weak, when the Doppler frequency islarge, when there is a plurality of arriving waves, or when theinterference wave strength is great, thereby enabling data quality to beattained. In the descriptions relating to the CDMA method, a pilotchannel and control channel have been described as examples ofconstantly transmitted signals, but this is not a limitation, and anysignal may be used as long as it is constantly transmitted. Also, themodulation method for signals transmitted by the base station has beendescribed as variable, but this is not a limitation, and it is alsopossible for the modulation method of signals transmitted by acommunication terminal to be made variable.

By means of the above, it is possible to configure a radio communicationsystem, transmitting apparatus, and receiving apparatus that use themethod described in Embodiment 1, and by this means, it is possible toimprove the reception sensitivity characteristics of a receivingapparatus. In this case, the description has referred to a combinationof three kinds of modulation methods—QPSK, 16QAM, and 64QAM—but thisembodiment is not limited to this, and neither is it limited toswitching between three kinds of modulation methods. Moreover, in FIG. 3and FIG. 13 it is also possible to input communication trafficinformation, for example, and to consider this in deciding on themodulation method. Furthermore, interference wave strength, fieldstrength, the multipath situation, and Doppler frequency have beendescribed as radio wave propagation environment parameters by way ofexamples, but this embodiment is not limited to these.

Embodiment 4

In Embodiment 4, a description is given of a radio communication system,transmitting apparatus, and receiving apparatus that use the methoddescribed in Embodiment 1.

The configuration of a base station transmitting apparatus according tothis embodiment is as shown in FIG. 2, and a detailed explanation ofthis configuration is omitted here. FIG. 23 shows the configuration ofthe receiving apparatus of a base station according to this embodiment.A receive radio section 2202 performs predetermined radio processing ona signal received via an antenna 2201, and outputs a received quadraturebaseband signal in-phase component and received quadrature basebandsignal quadrature phase component.

A synchronization section 2203 achieves time synchronization with acommunication terminal based on the received quadrature baseband signalin-phase component and received quadrature baseband signal quadraturephase component output from the receive radio section 2202, and outputsa synchronization signal to a detection section 2204.

The detection section 2204 performs detection processing using thereceived quadrature baseband signal in-phase component and receivedquadrature baseband signal quadrature phase component output from thereceive radio section 2202, and the synchronization signal output fromthe synchronization section 2203, and outputs a received digital signal.

An interference wave strength estimation section 2205 estimates theinterference wave strength from the received quadrature baseband signalin-phase component and received quadrature baseband signal quadraturephase component output from the receive radio section 2202, and outputsan interference wave strength estimation signal to a modulation methoddetermination section 2209.

A field strength estimation section 2206 estimates the field strengthfrom the received quadrature baseband signal in-phase component andreceived quadrature baseband signal quadrature phase component outputfrom the receive radio section 2202, and outputs a field strengthestimation signal to the modulation method determination section 2209.

A multipath estimation section 2207 estimates the multipath situationfrom the received quadrature baseband signal in-phase component andreceived quadrature baseband signal quadrature phase component outputfrom the receive radio section 2202, and outputs a multipath estimationsignal to the modulation method determination section 2209.

A Doppler frequency estimation section 2208 estimates the Dopplerfrequency from the received quadrature baseband signal in-phasecomponent and received quadrature baseband signal quadrature phasecomponent output from the receive radio section 2202, and outputs aDoppler frequency estimation signal to the modulation methoddetermination section 2209.

Based on the interference wave strength estimation signal, fieldstrength estimation signal, multipath estimation signal, and Dopplerfrequency estimation signal, the modulation method determination section2209 makes a decision so that, for example, QPSK is selected when thefield strength is weak, when the Doppler frequency is large, when thereis a plurality of arriving waves, or when the interference wave strengthis great, and outputs a control signal.

Next, a description will be given concerning the modulation method forinitial transmission by the base station. When a radio communicationsystem of the kind described in this embodiment is constructed, forexample, a communication terminal first transmits a transmit signal, thebase station receives the signal transmitted by the communicationterminal and estimates the radio wave propagation environment anddecides on the modulation method so that, for example, QPSK is selectedwhen the field strength is weak, when the Doppler frequency is large,when there is a plurality of arriving waves, or when the interferencewave strength is great. By determining the modulation method for initialtransmission in this way, data quality is improved at the communicationterminal. This initial setting of the modulation method is not limitedto this embodiment, and can be applied to communication methodscharacterized by switching of the modulation method according to theradio wave propagation environment, communication traffic, and so forth.

Similarly, with a communication method characterized by changing of theerror correction method according to the radio wave propagationenvironment, the same kind of approach can be taken to the errorcorrection method for initial transmission. With regard to the initiallyselected error correction method, a communication terminal firsttransmits transmit data, the base station receives the signaltransmitted by the communication terminal, estimates the radio wavepropagation environment, and decides on the error correction method sothat, for example, a method with good error correction capability isselected when the field strength is weak, when the Doppler frequency islarge, when there is a plurality of arriving waves, or when theinterference wave strength is great, and it is only necessary to decideon the error correction method for signals that the base stationtransmits.

Determining the error correction method for initial transmission asdescribed above enables data quality to be improved at the communicationterminal. This initial setting of the error correction method is notlimited to this embodiment, and can be applied to communication methodscharacterized by switching of the error correction method according tothe radio wave propagation environment, communication traffic, and soforth.

By means of the above, it is possible to configure a radio communicationsystem, transmitting apparatus, and receiving apparatus that use themethod described in Embodiment 1, and by this means, it is possible toimprove the reception sensitivity characteristics of a receivingapparatus. Moreover, in FIG. 3 and FIG. 13 it is also possible to inputcommunication traffic information, for example, and to consider this indeciding on the modulation method. Furthermore, interference wavestrength, field strength, the multipath situation, and Doppler frequencyhave been described as radio wave propagation environment parameters byway of examples, but this embodiment is not limited to these.

This embodiment does not depend on the multiplexing method, and may beimplemented in the same way with the CDMA method and OFDM method.

Embodiment 5

In Embodiment 5, a description is given of a transmitting apparatus andreceiving apparatus of the radio communication method of the presentinvention.

FIG. 24 shows an example of a frame configuration according to thisembodiment. With respect to time on the horizontal axis, reference code2301 denotes a preamble, comprising symbols by means of which thereceiving apparatus achieves time synchronization with the transmittingapparatus. Reference code 2302 denotes data symbols, the modulationmethod being variable. Reference code 2303 denotes pilot symbols forestimating transmission path distortion and frequency offset. Referencecode 2304 denotes control symbols for system control such as systeminformation and cell information.

FIG. 25 shows QPSK symbol and pilot symbol signal point arrangement inthe IQ plane according to this embodiment. Reference code 2401 indicatesFIG. 24 data symbol 2302 signal points, reference code 2402 indicatespreamble 2301 and control symbol 2304 signal points, and reference code2403 indicates the pilot symbol 2303 signal point. The reference code2402 and reference code 2403 signal point amplitudes—that is, distancesfrom the origin—are greater than the reference code 2401 signal pointamplitudes. As a result, the accuracy of estimation of transmission pathdistortion by means of the pilot symbol and the accuracy of frequencyoffset estimation are improved in the receiving apparatus. Moreover,control symbol noise tolerance is increased. Signal point arrangementshould be carried out so that use is possible with the method oftransmission power amplifier use described in Embodiment 1.

FIG. 26 shows 16QAM symbol and pilot symbol signal point arrangement inthe IQ plane. Reference code 2501 indicates FIG. 24 data symbol 2302signal points, reference code 2502 indicates preamble 2301 and controlsymbol 2304 signal points, and reference code 2503 indicates the pilotsymbol 2303 signal point. The reference code 2502, and reference code2503 signal point amplitudes—that is, distances from the origin—aregreater than the reference code 2501 maximum signal point amplitudes. Asa result, the accuracy of estimation of transmission path distortion bymeans of the pilot symbol and the accuracy of frequency offsetestimation are improved in the receiving apparatus. Moreover, controlsymbol noise tolerance is increased. Signal point arrangement should becarried out so that use is possible with the method of transmissionpower amplifier use described in Embodiment 1.

FIG. 27 shows 64QAM symbol signal point arrangement in the IQ planeaccording to this embodiment. Reference code 2601 indicates FIG. 23 datasymbol 2302 signal points, and the preamble 2301, pilot symbols 2303,and control symbols 2304 are taken as having one or other signal pointthat has the maximum amplitude shown by reference code 2602 in FIG. 27.

FIG. 28 shows the configuration of a transmitting apparatus according tothis embodiment. The parts in FIG. 28 identical to those in FIG. 3 areassigned the same codes as in FIG. 3 and their detailed explanations areomitted. Based on selected modulation method information contained in aninput control signal, a radio section 2701 controls the gain of thetransmit quadrature baseband signal in-phase component output from anin-phase component switching section 205 and the received quadraturebaseband signal quadrature phase component output from a quadraturephase component switching section 205, and outputs a transmit signal toa transmission power amplification section 207.

FIG. 29 shows the internal configuration of a signal generating section,indicating the detailed configuration of the QPSK signal generatingsection 201, 16QAM signal generating section 202, and 64QAM signalgenerating section 203 in FIG. 3 and FIG. 28.

In FIG. 29, a frame timing control section 2801 outputs a frame timingsignal that controls frame timing to a modulation signal generatingsection 2802, control signal generating section 2803, preamble signalgenerating section 2804, pilot signal generating section 2805, andsignal selection section 2806.

The modulation signal generating section 2802 generates a modulationsignal based on the frame timing signal frame configuration in the frametiming signal output from the frame timing control section 2801, andoutputs a data symbol transmit quadrature baseband signal to the signalselection section 2806.

The control signal generating section 2803 generates a control signalbased on the frame timing signal frame configuration in the frame timingsignal output from the frame timing control section 2801, and outputs acontrol signal transmit quadrature baseband signal to the signalselection section 2806.

The preamble signal generating section 2804 generates a preamble basedon the frame configuration of the frame timing signal output from theframe timing control section 2801, and outputs a preamble transmitquadrature baseband signal to the signal selection section 2806.

The pilot signal generating section 2805 generates a pilot signal basedon the frame configuration of the frame timing signal output from theframe timing control section 2801, and outputs a pilot signal transmitquadrature baseband signal to the signal selection section 2806.

The signal selection section 2806 selects a transmit quadrature basebandsignal to be output based on the frame timing signal frame configurationfrom among the data symbol transmit quadrature baseband signal outputfrom the modulation signal generating section 2802, the control signaltransmit quadrature baseband signal output from the control signalgenerating section 2803, the preamble transmit quadrature basebandsignal output from the preamble signal generating section 2804, thepilot signal transmit quadrature baseband signal output from the pilotsignal generating section 2805, and the frame timing signal output fromthe frame timing control section 2801, and outputs the selected transmitquadrature baseband signal.

Then, the fading distortion estimation section 304 shown in FIG. 4outputs a fading distortion estimation signal according to themodulation method based on the ratio of the pilot symbol signal pointamplitude and the maximum signal point amplitude of each modulationmethod. The details of the configuration will now be described usingFIG. 30. FIG. 30 shows the configuration of a receiving apparatusaccording to this embodiment. The parts in FIG. 30 identical to those inFIG. 4 are assigned the same codes as in FIG. 4 and their detailedexplanations are omitted.

A correction section 2901 calculates a correction value based on controlsignal modulation method information in the fading distortion estimationsignal output from the fading distortion estimation section 304 andinput control signal, multiplies the fading distortion estimation signalby the correction value, and outputs the corrected fading distortionestimation signal to the QPSK detection section 306, 16QAM detectionsection 307, and 64QAM detection section 308. At this time, thecorrection value is determined from the ratio of the pilot symbol signalpoint amplitude to the maximum signal point amplitude of each modulationmethod. By this means, the estimation accuracy of the fading distortionestimation signal is increased and the reception sensitivitycharacteristics of the receiving apparatus are improved.

According to the above-described embodiment, modulation signals of aplurality of modulation methods can be amplified by a common poweramplifier, and high-sensitivity reception can be achieved at thereceiving apparatus.

Embodiment 6

FIG. 31 shows an example of the frame configuration of a signaltransmitted by a base station according to Embodiment 6. In FIG. 31,with respect to the time and frequency axes, reference code 3001 denotesa data symbol, with, for example, QPSK, 16QAM, or 64QAM selectable asthe modulation method. Reference code 3002 denotes a pilot symbol, withthe pilot symbol signal point amplitude being variable in the IQ planeas described in Embodiment 1 according to the data symbol 3001modulation method.

FIG. 32 shows the configuration of the transmitting apparatus of a basestation according to this embodiment. In FIG. 32, a modulation section3101 carries out modulation using the selected modulation method on aninput transmit digital signal, based on modulation method and frameconfiguration information in an input control signal, and outputs aserial signal to a serial-to-parallel conversion section 3102.

The serial-to-parallel conversion section 3102 converts the serialsignal output from the modulation section 3101 to parallel form, andoutputs parallel signals to a discrete reverse Fourier transform section3103. The discrete reverse Fourier transform section 3103 performs adiscrete reverse Fourier transform on the parallel signals output fromthe serial-to-parallel conversion section 3102, and outputs the besignals after the discrete reverse Fourier transform to a radio section3104.

The radio section 3104 performs predetermined radio processing on thesignals output from the discrete reverse Fourier transform section 3103,and outputs a transmit signal to a transmission power amplificationsection 3105. The transmission power amplification section 3105amplifies the transmit signal output from the radio section 3104, andtransmits the amplified transmit signal to a communication terminal viaan antenna 3106.

FIG. 33 shows the configuration of the receiving apparatus of acommunication terminal according to this embodiment. In FIG. 33, a radiosection 3202 performs predetermined radio processing on a signalreceived via an antenna 3201 (received signal), and outputs theresulting signal to a Fourier transform section 3203. The Fouriertransform section 3203 performs a Fourier transform on the signal outputfrom the radio section 3202, and outputs parallel signals to aparallel-to-serial conversion section 3204.

The parallel-to-serial conversion section 3204 performsparallel-to-serial conversion of the parallel signals output from theFourier transform section 3203, and outputs a serial signal. Aninterference wave strength estimation section 3205 estimatesinterference wave strength based on the serial signal (a pilot symbol,for example) output from the parallel-to-serial conversion section 3204,and outputs an interference wave strength estimation signal to a radiowave propagation environment estimation section 3209.

A field strength estimation section 3206 estimates the field strengthbased on the serial signal (a pilot symbol, for example) output from theparallel-to-serial conversion section 3204, and outputs a field strengthestimation signal to the radio wave propagation environment estimationsection 3209. A multipath estimation section 3207 estimates the numberof arriving waves based on the serial signal (a pilot symbol, forexample) output from the parallel-to-serial conversion section 3204, andoutputs a multipath estimation signal to the radio wave propagationenvironment estimation section 3209.

A Doppler frequency estimation section 3208 estimates the Dopplerfrequency based on the serial signal (a pilot symbol, for example)output from the parallel-to-serial conversion section 3204, and outputsa Doppler frequency estimation signal to the radio wave propagationenvironment estimation section 3209.

The radio wave propagation environment estimation section 3209determines a request for the modulation method of a signal to betransmitted by the base station based on the interference wave strengthestimation signal, field strength estimation signal, multipathestimation signal, and Doppler frequency estimation signal, and outputsthis as a radio wave propagation environment estimation signal.Alternatively, the radio wave propagation environment estimation section3209 may output the interference wave strength estimation signal, fieldstrength estimation signal, multipath estimation signal, and Dopplerfrequency estimation signal themselves as radio wave propagationenvironment estimation signals. Radio wave propagation environmentestimation signal information is then transmitted from the transmittingapparatus of the communication terminal to the base station, and themodulation method of signals transmitted by the base station is changed.However, if the interference wave strength estimation signal, fieldstrength estimation signal, multipath estimation signal, and Dopplerfrequency estimation signal themselves are output as radio wavepropagation environment estimation signals, determination of themodulation method is carried out by the base station.

A distortion estimation section 3210 estimates distortion produced dueto the transmission path based on the serial signal (a pilot symbol, forexample) output from the parallel-to-serial conversion section 3204, andoutputs a distortion estimation signal to a correction section 3211. Thecorrection section 3211 multiplies the distortion estimation signaloutput from the distortion estimation section 3210 by a value thatvaries the amplitude of pilot symbols 3002 in the IQ plane according tothe modulation method of data symbols 3001 in FIG. 30 as a correctionvalue, and outputs the corrected distortion estimation signal to ademodulation section 3212. The demodulation section 3212 demodulates theserial signal output from the parallel-to-serial conversion section 3204based on the corrected distortion estimation signal output from thecorrection section 3211, and outputs a received digital signal.

FIG. 34 shows the internal configuration of the modulation section 3101in FIG. 32. In FIG. 34, in a QPSK serial signal generating section 3301,when modulation method information contained in a control signal amonginput transmit digital signals and control signals is QPSK, a serialsignal is generated in accordance with the frame configuration in FIG.31, and a QPSK serial signal is output to a serial signal selectionsection 3304.

In a 16QAM serial signal generating section 3302, when modulation methodinformation contained in a control signal among input transmit digitalsignals and control signals is 16QAM, a serial signal is generated inaccordance with the frame configuration in FIG. 31, and a 16QAM serialsignal is output to the serial signal selection section 3304.

In a 64QAM serial signal generating section 3303, when modulation methodinformation contained in a control signal among input transmit digitalsignals and control signals is 64QAM; a serial signal is generated inaccordance with the frame configuration in FIG. 31, and a 64QAM serialsignal is output to the serial signal selection section 3304.

The serial signal selection section 3304 has a QPSK serial signal, 16QAMserial signal, 64QAM serial signal, and control signal as input, selectsthe serial signal of the specified modulation method based on modulationmethod information contained in the control signal, and outputs this asthe selected serial signal. The serial signal selected at this timecorresponds to the serial signal output from the modulation section 3101in FIG. 32.

As in Embodiment 1, the QPSK serial signal generating section 3301,16QAM serial signal generating section 3302, and 64QAM serial signalgenerating section 3303 operate so that the respective average power ofthe respective transmit signals is fixed, and, in the transmission poweramplification section 3106, pilot symbol signal point amplitudes arearranged in the in-phase-quadrature plane so that the operating rangedoes not vary even if the modulation method is switched. Also, in thetransmission power amplification section 3106, pilot symbol signal pointamplitudes may be arranged in the IQ plane so that the receptionsensitivity of the communicating party is made optimal within a range inwhich distortion does not arise.

FIG. 35 shows the configuration of the transmitting apparatus of a basestation according to this embodiment. FIG. 35 differs from FIG. 32 inthat a control signal is input to the radio section 3401. The radiosection 3401 has a function for performing adjustment so that theaverage transmission power of a transmit signal is the same with anymodulation method based on modulation method information contained inthe input control signal.

By means of the above, it is possible for the modes described inEmbodiment 1, Embodiment 2, and Embodiment 5 also to be implemented withthe OFDM method.

Embodiment 7

In Embodiment 7, a case is described in which, changing the standpointfrom that of the method described in Embodiment 1, the focus is onimproving the reception sensitivity characteristics of the receivingapparatus, and data transmission is performed with the maximumtransmission output power made the same for each modulation method in aradio communication method in which adaptive modulation is carried out.

The transmitting apparatus of this embodiment has the configurationshown in FIG. 3, and differs from Embodiment 1 in the way in whichtransmission power is amplified. Moreover; the receiving apparatus hasthe configuration shown in FIG. 13, and therefore descriptions of therespective configurations are omitted here. FIG. 36 is a graph showingthe input/output relationship of a transmission power amplificationsection according to this embodiment. In FIG. 36, reference code 3601indicates the 64QAM operation point, reference code 3602 indicates the16QAM operation point, and reference cede 3603 indicates the QPSKoperation point, signifying that the average transmission output powerdiffers for each modulation method. Further, reference code 3604indicates the QPSK operating range, reference code 3605 indicates the16QAM operating range, and reference code 3606 indicates the 64QAMoperating range, the operating range being the same for each modulationmethod.

Using a transmission power amplifier that performs power amplificationas described above makes it possible to improve the receptionsensitivity characteristics of the receiving apparatus. Also, with atransmitting apparatus that has the configuration shown in FIG. 10, thetransmitting apparatus can be made smaller than when using atransmission power amplifier as appropriate for each modulation method.

Next, a case will be described in which a service mode is implementedthat is characterized by having a different service range for eachmodulation method within the service area of a base station equippedwith the power amplifier described in this embodiment.

FIG. 37 is a conceptual diagram showing the range in which communicationfrom a base station is possible for each modulation method. In FIG. 37,of the signals transmitted from the base station 3701, signals modulatedusing 64QAM can be communicated within the area whose boundary isindicated by reference code 3702, and this area is designated the 64QAMservice area 3702. Similarly, of the signals transmitted from the basestation 3701, signals modulated using 16QAM can be communicated withinthe area whose boundary is indicated by reference code 3703, and thisarea is designated the 16QAM service area 3703; and of the signalstransmitted from the base station 3701, signals modulated using QPSK canbe communicated within the area whose boundary is indicated by referencecode 3704, and this area is designated the QPSK service area 3704.

The ability to divide the service area for each modulation method inthis way derives from the fact that, as can be seen from FIG. 36, 64QAMhas lower average transmission output power than the other modulationmethods, incurs few transmission path errors in narrow-areacommunications, and is suited to high-speed communication. QPSK, on theother hand, has higher average transmission output power than the othermodulation methods, and incurs few transmission path errors even inwide-area communications, making it suitable for low-speed datacommunication and voice communication.

By means of the above, it is possible to make the maximum transmissionoutput power the same for each modulation method in a radiocommunication method whereby adaptive modulation is performed, and inaddition, it is possible to implement a service mode characterized byhaving a different service area for each modulation method.

Embodiment 8

In Embodiment 8, a case is described in which the average transmissionoutput power permitted in a radio communication system is stipulatedwhen data transmission is performed with the maximum transmission outputpower made the same for each modulation method described in Embodiment7.

When the maximum transmission output power of each modulation method ismade the same, it may be that, for example, the average transmissionoutput power for QPSK is 2 W, the average transmission output power for16QAM is 1 W, and the average transmission output power for 64QAM is 0.5W.

On the other hand, if the average transmission output power stipulatedin a radio communication system is in the range from 0.25 W to 3.00 W,the average transmission output power of each modulation method will bewithin the stipulated average transmission output power range even ifthe maximum transmission output power of each modulation method is madethe same.

However, if the average transmission output power stipulated in a radiocommunication system is in the range from 0.25 W to 1.50 W, when themaximum transmission output power of each modulation method is made thesame, the average transmission output power for QPSK will be 2 W, andwill no longer fall within the stipulated range.

In this case, the condition for keeping the QPSK average transmissionoutput power within the stipulated range and enabling signals of eachmodulation method to be amplified by the transmission poweramplification section is a value of 1.5 W.

When the average transmission output power in a radio communicationsystem is stipulated in this way, this must be taken into consideration,and the maximum transmission output power for each modulation methodwill not necessary be the same at this time.

As described above, according to the present invention, in a radiocommunication method whereby adaptive modulation is performed, thereception sensitivity characteristics of a receiving apparatus can beimproved by maintaining the average transmission power of a transmittingapparatus at a fixed level, and arranging pilot symbol signal points inthe IQ plane so that the reception sensitivity characteristics of thereceiving apparatus are made optimal.

The present invention is not limited to the above described embodiments,and various variations and modifications may be possible withoutdeparting from the scope of the present invention.

This application is based on Japanese Patent Application No. 2000-320624filed on Oct. 20, 2000, Japanese Patent Application No. 2000-337114filed on Nov. 6, 2000, Japanese Patent Application No. 2001-51829 filedon Feb. 27, 2001, and Japanese Patent Application No. 2001-245052 filedon Aug. 10, 2001, entire content of which is expressly incorporated byreference herein.

The invention claimed is:
 1. A transmitting apparatus, comprising: amodulation signal generator that generates a modulation signal bymodulating transmission data selecting one of a plurality of modulationschemes according to a frame timing signal, a first modulation scheme ofthe plurality of modulation schemes having a higher m-ary modulationvalue than other modulation schemes of the plurality of modulationschemes; a pilot signal generator that generates a pilot signal byselecting one of a plurality of amplitudes according to the frame timingsignal; an orthogonal frequency division multiplexing (OFDM) signalgenerator that generates an OFDM signal by selecting the modulationsignal and the pilot signal according to the frame timing signal; aradio converter that converts the OFDM signal to a radio signal; anamplifier that amplifies the radio signal; and an antenna that transmitsthe amplified radio signal, wherein the pilot signal is inserted in theOFDM signal per a predetermined OFDM symbol and per a predeterminedsubcarrier and has a lower amplitude than a maximum amplitude of thefirst modulation scheme in an in-phase-quadrature (IQ) plane.
 2. Thetransmitting apparatus according to claim 1, wherein the amplitude ofthe pilot signal is determined according to the used modulation scheme.3. The transmitting apparatus according to claim 1, wherein theamplitude of the pilot signal is determined according to a bit errorrate in a receiving apparatus.
 4. The transmitting apparatus accordingto claim 1, wherein the amplitude of either a quadrature phase componentor an in-phase component of the pilot signal is zero.
 5. Thetransmitting apparatus according to claim 1, wherein the frame timingsignal controls a time when a frame including the modulation signal andthe pilot signal is generated.
 6. The transmitting apparatus accordingto claim 1, wherein the first modulation scheme is 64QAM.
 7. Atransmitting method, comprising: generating a modulation signal bymodulating transmission data selecting one of a plurality of modulationschemes according to a frame timing signal, a first modulation scheme ofthe plurality of modulation schemes having a higher m-ary modulationvalue than other modulation schemes of the plurality of modulationschemes; generating a pilot signal by selecting one of a plurality ofamplitudes according to the frame timing signal; generating anorthogonal frequency division multiplexing (OFDM) signal by selectingthe modulation signal and the pilot signal according to the frame timingsignal; converting the OFDM signal to a radio signal; amplifying theradio signal; and transmitting the amplified radio signal from anantenna, wherein the pilot signal is inserted in the OFDM signal per apredetermined OFDM symbol and per a predetermined subcarrier and has alower amplitude than a maximum amplitude of the first modulation schemein an in-phase-quadrature (IQ) plane.
 8. The method according to claim7, wherein the amplitude of the pilot signal is determined according tothe used modulation scheme.
 9. The method according to claim 7, whereinthe amplitude of the pilot signal is determined according to a bit errorrate.
 10. The method according to claim 7, wherein the amplitude ofeither a quadrature phase component or an in-phase component of thepilot signal is zero.
 11. The method according to claim 7, wherein theframe timing signal controls a time when a frame including themodulation signal and the pilot signal is generated.
 12. The methodaccording to claim 7, wherein the first modulation scheme is 64QAM. 13.A receiving apparatus, comprising: an antenna that receives a radiosignal; an orthogonal frequency division multiplexing (OFDM) signalconverter that converts the radio signal to an OFDM signal; an estimatorthat generates a distortion estimation signal which estimatestransmission path distortion using a pilot signal, which was generatedby selecting one of a plurality of amplitudes according to a frametiming signal, included in the OFDM signal; and a demodulator thatcorrects a distortion of the radio signal using the distortionestimation signal and demodulates transmission data, wherein: the OFDMsignal includes a modulation signal obtained by modulating thetransmission data using a selected one of a plurality of modulationschemes according to the frame timing signal and the pilot signal; afirst modulation scheme of the plurality of modulation schemes has ahigher m-ary modulation value than other modulation schemes of theplurality of modulation schemes; and the pilot signal is inserted in theOFDM signal per a predetermined OFDM symbol and per a predeterminedsubcarrier and has a lower amplitude than a maximum amplitude of thefirst modulation scheme in an in-phase-quadrature (IQ) plane.
 14. Areceiving apparatus according to claim 13, wherein an amplitude ofeither a quadrature phase component or an in-phase component of thepilot signal is zero.
 15. A receiving method, comprising: receiving aradio signal by an antenna; converting the radio signal to an orthogonalfrequency division multiplexing (OFDM) signal; generating a distortionestimation signal which estimates transmission path distortion using apilot signal, which was generated by selecting one of a plurality ofamplitudes according to a frame timing signal, included in the OFDMsignal; and correcting a distortion of the OFDM signal using thedistortion estimation signal and demodulating transmission data; theOFDM signal includes a modulation signal obtained by modulating thetransmission data using a selected one of a plurality of modulationschemes according to the frame timing signal and the pilot signal; afirst modulation scheme of the plurality of modulation schemes has ahigher m-ary modulation value than other modulation schemes of theplurality of modulation schemes; and the pilot signal is inserted in theOFDM signal per a predetermined OFDM symbol and per a predeterminedsubcarrier and has a lower amplitude than a maximum amplitude of thefirst modulation scheme in an in-phase-quadrature (IQ) plane.
 16. Themethod according to claim 15, wherein the amplitude of either aquadrature phase component or an in-phase component of the pilot signalis zero.